Watercolor paper is a touchy subject to discuss but it is the most important art supply for watercolor painting. Even at the beginning of your watercolor endeavors, painting on good quality paper will make learning painting less frustrating and give you better results.
Shopping for watercolor paper is confusing! There are a zillion brands of watercolor paper for sale in a wide variety of prices and forms. To simplify your paper shopping DO NOT buy the cheapest paper. Please buy the best paper you can afford. Canson and Strathmore make some decent inexpensive watercolor paper pads. If you can buy your paper at an art supply store online You’ll probably get a better price then at one of the big box retail stores that offer coupons and sales and blow up the price of the supplies so they can offer you a coupon discount.
After 25 years of watercolor painting and teaching I have found Arches Watercolor paper to be the best. Specifically I use 140 lb. Cold Pressed Arches paper. It is sometimes called NOT Pressed. I buy my paper in 22” x 30” sheets then cut it down to whatever size I want. You can find this paper sold in smaller pads and blocks as well.
If you hang out with other watercolor painters or are in a class you could purchase the sheets in bundles of 5, 10 or 20 sheets and divide it up.
I buy my paper online from Jackson’s Art Supplies in London! The prices are good even with the shipping from Europe and the paper arrives in 2 days! Here is a link to their website: https://www.jacksonsart.com/en-us/arches-aquarelle-140lb-300gsm-22x30in-56x76cm-5-sheets-not?___store=jacksonsart_us&acc=31839b036f63806cba3f47b93af8ccb5
While you are perusing Jackson’s site, check out their selection of Pro-Arte watercolor paint brushes, I use those and like them a lot.
Even if you are nervous about shopping in London and shipping charges, Jacksons will give you. 10% discount on your first order.